What is Sodium Metabisulfite Used for and How Does it Work?
In water treatment, sodium metabisulfite is often used in the dechlorination stage.

Before we begin, since sodium metabisulfite is known by many names, we will start by introducing the most common names.

  • Sodium Pyrosulfite
  • Disulfurous acid
  • SMBS

*Note that the term "sodium" can be exchanged for " caustic ".

Its uses

This versatile product can be used as an antioxidant, food preservative, and even for photographic processing. As we are a water treatment company, we will only discuss its uses as an antioxidant in water treatment.


In the water treatment industry, sodium metabisulfite has many uses. Starting with its use as a reducer since it is often used as a deoxygenator. Then, its antioxidant capacity makes it an important part of the dechlorination stage or even during the pre-treatment of reverse osmosis.

Indeed, sodium metabisulfite is very efficient for the reduction of free chlorine and chloramine. This is why they are often used for dechlorination or in the pretreatment of reverse osmosis. It should be noted that the importance of chloramine removal prior to reverse osmosis treatment lies in the durability of osmotic membranes. To learn more about this subject, you can read this article.


In short, to learn more about sodium metabisulfite, we invite you to read this article presenting a comparison between 3 dechlorination technologies: activated carbon, sodium metabisulfite and UV irradiation.

How does SBMS work?

Simply put, the addition of sodium metabisulfite to water activates a chemical reaction that immediately attacks the targeted contaminant. As an example:

For free chlorine: Na2S2O5 + 3H2O + 2Cl2 -> NaHSO4 + 2HCl

For Chloramines: Na2S2O5 + 9H2O + 2NH3 +6Cl2 -> 6NaHSO4 + 10HCl + 2NH4Cl

in FAQ
What is Water Disinfection
Disinfection, whether it refers to water or otherwise, is defined as a procedure to eliminate or kill microorganisms or deactivate unwanted viruses. In other words, the term disinfection is a generic term that refers to any procedure aimed at reducing bacteria, viruses and protozoa.